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5C and Image Constraint--A New Interpretation  

post #1 of 4
Thread Starter 
In the discussion of the upcoming JVC D-Theater encoded HD D-VHS tapes, someone wondered about why we thought the tapes would be image constrained when viewed through the HD analog outputs on the decks. In response, I quoted the relavant text of the DTCP Adopter's Agreement (the entire text of which you can find here)--first, from the definitions, on page 24 of the PDF file:
Quote:
2.8 “Constrained Image†shall mean an image having the visual equivalent of no more than 520,000 pixels per frame (e.g., an image with resolution of 960 pixels by 540 pixels for a 16:9 aspect ratio). A Constrained Image may be attained by reducing resolution, for example, by discarding, dithering, or averaging pixels to obtain the specified value. A Constrained Image can be displayed using video processing techniques such as line doubling or sharpening to improve the perceived quality of the image. By way of example, a Constrained Image may be stretched or doubled, and displayed full-screen, on a 1000-line monitor.
2.12 “Decrypted DT Data†shall mean, with respect to any Licensed Product, DT Data that has been received by such Licensed Product’s Sink Function and decrypted by such Licensed Product according to DTCP but has not been (a) protected by a one-generation copy protection technology identified or approved by DTLA pursuant to Sections 2.2.1.1 or 2.2.1.3 of Part 1 of this Exhibit B; (b) protected by a technology approved by DTLA pursuant to Section 4.4.4 of Part 1 of this Exhibit B or (c) passed to an output permitted by Part 1 of this Exhibit B.
2.13 “DT Data†shall mean Commercial Entertainment Content that has been encrypted and transmitted using DTCP. For avoidance of doubt, DT Data includes Decrypted DT Data.
2.15 “EPN Field†shall mean the field or bits, described in the Specification, used to indicate that Commercial Audiovisual Content is to be protected using DTCP but that copy control restrictions are not being asserted over such content.
Then, from the beginning of section 4, at the bottom of page 28:
Quote:
4. SINK FUNCTION PERMITTED OUTPUTS
4.1 Generally. As set forth in more detail below, a Licensed Product shall not pass Decrypted DT Data, whether in digital or analog form, to an output except as permitted below.
4.1.1 Outputs, Video. A Licensed Product shall not pass any representation or conversion of the video portion of Decrypted DT Data to any output except:
4.1.1.1 Where Decrypted DT Data is output via an approved standard definition analog output in a manner pursuant to Section 4.2 of this Part of this Exhibit B;
4.1.1.2 Where Decrypted DT Data is output in a High Definition Analog Form in a manner pursuant to Section 4.3 of this Part of this Exhibit B;
4.1.1.3 Where Decrypted DT Data is output via a digital output in a manner pursuant to Section 4.4 of this Part of this Exhibit B; or
4.1.1.4 Where the Decrypted DT Data is encoded Copy Freely with the EPN Field unasserted, in which case there are no restrictions on output.
Onward to section 4.3, near the top of page 30:
Quote:
4.3 High Definition Analog Output. Licensed Products shall not pass Decrypted DT Data to a High Definition Analog Output, except as set forth in this Section 4.3:
4.3.1 Licensed Products may pass Decrypted DT Data to a High Definition Analog Output as a Constrained Image.
4.3.2 Licensed Products that recognize and respond to the Image Constraint Token in accordance with the Specification may pass Decrypted DT Data to an output in High Definition Analog Form when authorized by the setting of the Image Constraint Token.
4.3.3 Licensed Products incorporated into Computer Products may pass Copy One Generation or No More Copies Decrypted DT Data without image constraint to SVGA (1024x768 and greater),
XGA(1024x768), SXGA and UXGA or similar computer video outputs that were widely implemented as of May 1, 2001 (but not to such typical consumer electronics outputs as NTSC, PAL, SECAM, SCART, YUV, S-Video and consumer RGB, whether or not such outputs are found on any Computer Product) in High Definition Analog Form for devices manufactured prior to December 31, 2005, unless otherwise notified by DTLA.
4.3.4 Licensed Products may pass Decrypted DT Data in High Definition Analog Form to a High Definition Analog Output where such Decrypted DT Data is encoded Copy Freely.
Finally, at the bottom of page 33:
Quote:
2.2 Image Constraint. Adopter acknowledges that Content Participants are not permitted to encode, or direct to be encoded, Commercial Audiovisual Content so as to require Decrypted DT Data to be output as a Constrained Image except with respect to Prerecorded Media, Pay Television Transmission, Video-on-Demand, Subscription-on-Demand, Pay-Per-View, a new business model comparable to any of the foregoing or any other Conditional Access Delivery of a Program that (i) had a theatrical release or was released direct-to-video and (ii) is transmitted or delivered uninterrupted by Commercial Advertising Messages. Licensed Products that have a Source Function (a “Source Deviceâ€) shall set, in accordance with the Specification, the Image Constraint Token associated with a Program so as to permit any Licensed Product with a Sink Function to output such Program in High Definition Analog Form if such Source Device outputs such Program in unprotected High Definition Analog Form other than as permitted in Section 4.3.3 of Part 1 of Exhibit B. In addition, a Source Device shall set, in accordance with the Specification, the Image Constraint Token associated with a Program so as to permit any Licensed Product with a Sink Function to output such Program in High Definition Analog Form if such Program was not specifically encoded to output such Program as a Constrained Image when received by the Source Device.
As I read back over these sections, it occurs to me that the contents of prerecorded tapes and other media does not fit the description of "DT Decrypted Data" (i.e., data that was received over 5C and decrypted) and as such is not subject to the rules. The source device can do anything it wants with it--it could send it out with any level of protection over 1394/DTCP and send it unconstrained through analog HD outputs, if it so desired. The same actually applies to information received over cable or DBS (except for DFAST encoded cable content, which has a specified relationship with DTCP)--a cable or DBS STB receiving content encrypted in some other fashion can output the video as it pleases, even if also outputs it digitally, encrypted with DTCP. The behavior of the STB is entirely up to the service providers and the security requirements of the people who supply content to them.

In similar fashion, the HDCP license agreement does not dictate the behavior of the content source at all--it just details what devices which receive HDCP-encrypted data are allowed to do with it after they decrypt it.

A recording of copy-protected content from an STB connected to a deck, PVR or other recording device via 1394/DTCP would qualify as "DT Decrypted Data", having been received encrypted with DTCP.

Now, this isn't to say that prerecorded media player and HD cable and DBS STB OEMs won't do something draconian with output through HD analog connections (if they even choose to supply them), but it would appear that they are not compelled to do it by the DTCP Adopter's Agreement, and I'd previously thought.

-- Mike Scott
post #2 of 4
Mike -

I believe (and have always believed) that neither DTCP or HDCP much restricts what a source device can do.

But the reason that analog output from D-VHS tapes will probably (I have no definite knowledge) be image constrained is because, as we all know, Hollywood wants it that way. And I have not seen anything to suggest they have yet backed down on that part.

But maybe we will be pleasantly surprised. ;)

- Tom
post #3 of 4
Mike is correct that 5C/DTCP does not dictate the level of protection of the content on media. From 5C-enabled only hardware level, the source device encrypts the content which is the compressed MPEG data (or in other format), the sink device decrypts the data stream and produces the same compressed data and if permitted, will record/display it.

I would not surprise that 5C alone is not good enough for Hollywood and that may be one of the reasons for slow acceptance of firewire and lack of pre-recorded HD movies. D-Theater (or equivalence) is basically another layer of protection of media content which can only be read or created by D-Theater licensed devices.

It is inevitable that D-Theater or something else will emerge as the standard for DVSH, HD-DVD or HD-PVR. We may learn to live with it.
post #4 of 4
Thanks for the clarification Mike. It seems to make sense that studios will likely be enabling output through the component connector, if only from a purely financial motive; who would buy into this this year if it needed 1394.

I wish I had the brainpower needed to sift through these spec docs, but it's very helpful that you and others are taking the time to do this and give feedback the forum. Thanks.

Greg
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